Wave Drift Force - Newman’s method Calculation of wave drift forces from wave drift force coefficients using Newman’s method (approximation). The wave drift force coefficients corresponds to the frequency diagonal of the difference-frequency quadratic transfer function (QTF). See also description of theory in Simplified wave drift force model. By checking the Enable wave-current interaction checkbox, the zero-current wave drift force coefficients will be modified using Aranha’s formula. The wave drift force coefficients modified by current can be plotted based on current-velocity and -direction values entered in the wave-current correction preview window. These values only have effect in the plot. During a simulation, the actual current condition is used. Checking Enable wave-current interaction will only enable the excitation part of the wave-current interaction. To include the damping effect due to body velocities, a wave drift damping model should be added. See also Wave-current correction of second order wave drift force and wave drift damping using an extended Aranha’s formula. The validity of Newman’s approximation gets poorer for systems and degrees of freedom with a relatively low-natural period, or when the QTF-surface changes rapidly close to the main diagonal. When Newman’s approximation is not valid, a full Difference-Frequency QTF should be used instead. Usually, the running time of simulations with a full QTF is approximately the same as with Newman’s approximation, and the results are more accurate. Soil Penetration Wave Drift Force - from full Difference-Frequency Quadratic Transfer Function (QTF)